How to become an editor? (in literature)?

I've always been an avid reader; moreover, as I got older, I've loved to dissect the meanings and subtleties of books. I've loved writing for a while now, and I'm no novice to proofreading and editing my own works. How could I become an editor, aside from the bachelors degree? What sort of classes in college would I need to take, and what would be recommended as a form of supplemental education? What exactly does the editing process entail? Is it more correcting spelling and grammar, or correcting word choice and sentence structure? Do you have to work your way up in a publishing company?